Color tv phase comparator and fm detector circuits utilizing vacuum tube intermittently operating in secondary emission mode



NOV- 8, 1966 D. R. TAYLOR, JR 3,284,565

COLOR Tv PHASE COMPARATOR AND EM DETECTOR CIRCUITS UTILIZING VACUUM TUBEINTERMITTENTLY OPERATING IN SECONDARY EMISSION MODE Filed July ll, 19655 Sheets-Sheet l INV ENTOR4 pom/. A. ma a@ JR.

BY@ EJB-MAA 7' 7 GRA/EY Nov. 8, 1966 D R. TAYLoR, JR 3,284,565

VCOLOR TV PHASE COMPARATOR AND FM DETECTOR CIRCUITS UTILIZING VACUUMTUBE INTERMITTENTLY OPERATING IN SECONDARY EMISSION MODE Filed July l1,1963 5 Sheets-Sheet 2 i@ l 22 I o l I y F 2 INVENTOR.

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22M fw- NOV- 8, 1966 D. R. TAYLOR, JR 3,284,565

COLOR TV PHASE COMPARATOR AND FM DETECTOR CIRCUITS UTILIZING VACUUM TUBEINTERMITTENTLY OPERATING IN SECONDARY EMISSION MODE Filed July l1, 19655 Sheets-Sheet 3 BYgeMS'/m Nov. 8, 1966 D. R. TAYLOR, JR COLOR TV PHASECOMP UTILIZING VACUUM TUBE INTERMITTENTLY OPERATING IN SECONDARYEMISSION MODE Filed July l1, 1963 ARATOR AND FM DETECTOR CIRCUITS Nov.8, 1966 D. R. TAYLOR, JR 3,284,565 COLOR TV PHASE COMPARATOR AND FMDETECTOR CIRCUITS UTILIZING VACUUM TUBE INTERMITTENTLY OPERATING INSECONDARY EMISSION MODE Filed July ll, 1963 5 Sheets-Sheet 5 INVENTQR,a/ww A. myn/g JE,

Patented Nov. 8, 1966 3,284,565 COLOR TV PHASE COMPARATOR AND FM DE-TECTOR ClRCUITS UTILIZING VACUUM TUBE INTERMITTENTLY OPERATING llNSECOND- ARY EMISSION MODE v Donald R. Taylor, Jr., Philadelphia, Pa.,assignor to Philco Corporation, Philadelphia, Pa., a corporation ofDelaware Filed July 1I, 1963, Ser. No. 294,284 Claims. '(Cl. 178-5.4)

This invention relates to a novel and improved phase discriminatorcircuit and more particularly to a phase discriminat'or whose principleof operation includes a vacuum tube current reversal or secondaryemission effect of the type rst -discussed in my previous application,Serial No. 190,114, filed April 25, 1962, entitled Synchronizing SignalSeparator Making Use of Forward and Reverse Space Charge Currents, nowPatent 3,192,314, granted I une 29, 1965 and assigned to the presentassignee.

A Iphase detector or discriminator is a circuit which functions toproduce a D.C. output signal whose polarity and magnitude arerespectively indicative of the sign and magnitude of the phasedifference between plural A.C. input signals. Such discriminators havetaken diversified forms and nd application in a variety `of systems,including control circuitry, television, etc.

The current reversal or secondary emission effect above referred torelates to the principle of operation of multigrid vacuum tubes whereina reverse or secondary emission current will flow if the conventionalsupressor grid is made more positive than the conventional plate whencertain other conditions are satisfied. More particularly, a vacuum tubehaving a control grid, one or more intermediate grids, a last grid, anda plate may be operated in alternate secondary emission and normalconduction modes if the tube is biased into conduction at the first orcontrol grid, a B+ potential is applied to one of the intermediategrids, and respective signals are applied to the last grid and theplate. When the plate is more Dositive than the last grid, conventionalplate current will ow. When the last grid is the more positive, reverseor secondary emission current will flow in the plate. The presence andmagnitude of the normal and reverse plate currents may be respectivelycontrolled by the presence and magnitude of the signal at the firstgrid.

If the signals on the rst grid, last grid and plate are arranged so thatthe normal and reverse plate currents average to zero at a referencephase relationship between two of the signals, then at other phaserelationships an unbalanced alternating current, indicative of the signand magnitude of the phase relationship, will flow. If thesignal-frequency components are filtered from this net plate current, abipolar phase-indicative signal may be obtained.

In addition to a `basic /phase discriminator utilizing this secondaryemission effect, several exemplary ramifications thereof will bedescribed. A color TV chroma reference discriminator or combined burstkeyer-chrorna reference discriminator may be easily and simply providedutilizing the principles of the invention. Also a novel combined FMlimiter-discriminator Will be shown and discussed.

OBJECTS Accordingly the objects of the present invention are:

(1) To provide a novel and improved phase discriminator,

(2) To provide a novel mode of operation of multi-grid vacuum tubes,

(3) To provide new and improved chroma reference discriminator circuits,and

(4) To provide a new FM limiter-discriminator circuit.

Other objects and advantages of the invention will become apparent froma consideration of the following description thereof and accompanyingdrawings.

SUMMARY According to one embodiment of the present invention two A.C.signals are applied to the circuit of the invention for phase comparisonand a third, phase-indicative, signal is obtained at the output of saidcircuit. One of the A.C. Signals is utilized to turn on a multi-gridtube on positive half cycle intervals thereof. Two versions of the otherof the A.C. signals are applied to the plate and last grid,respectively, of the tube at phase angles such that normal and secondaryemission currents alternately flow in the plate circuit. These currentsaverage to zero when the two original AC. signals are in phase. Thephase indicative signal is recovered, via a filter, from the alternatingcurrent in the plate of the tube.

DRAWINGS FIG. la shows a basic phase discriminator circuit according tothe invention;

FIG. 1b is a diagram of waveforms found in the circuit of FIG. la;

FIGS. 2a, 2b, and 2c show diagrams of waveforms found in modificationsof the circuit of FIG. la;

FIG. 3 shows a chroma reference-discriminator burstkeyer according tothe invention;

FIG. 4a shows a schematic diagram of a FM limiterdiscriminator accordingto the invention;

FIGS. 4b and 4c show diagrams of waveforms and waveform vectors found inthe circuit of FIG. 4a;

FIG. 5a shows a schematic diagram of a modification of the circuit ofFIG. 4a; and

FIG. 5b shows diagrams of voltage vectors found in the circuit of FIG.5a.

FIG. ltr-PHASE DISCRIMINATOR Description The circuit depicted in FIG. 1ais a basic circuit of the invention which compares the signals generatedby sources 1i) and 12 to produce a voltage at output 14 whose polarityindicates whether the signal from source i2 (arbitrarily designated pBsignal) leads yor lags the signal from source Il) (arbitrarilydesignated qbA signal), and whose magnitude indicates the degree ofphase difference between the A and qb signals.

The bA signal is retarded in phase yby 45 in phase shifter 16 and isapplied to grid #l of pentode 18 via RC -circuit 20. One cycle of theresultant signal appearing on the first grid of pentode 18 is depictedas waveform egl in FIG. 1b. The 95A signal from source 1t) (not shown)is substantially identical to signal egl, except that its phase positionis 45 ahead of egl. RC circuit 20 is a familiar self-bias circuit whichis arranged to bias pentode 18 so that only the positive portion ofsignal egl turns pentode I8 on. Other methods of biasing lpentode 18 tosecure a similar result, which are well known to the skilled artisan,may be used in lieu of RC circuit 20.

The qbB signal is applied to grid #3 (the suppressor) of pentode 18 via90 phase shifter 26 and capacitor 22, and to the plate of pentode i8 viacapacitor 24. Although the suppressor and 4plate of pentode 18 do notperform their conventional functions in the circuit of FIG. 1a, thesenames will be retained and the signals present on these elements will berespectively designated es and ep. One cycle of each of these signals isdepicted in FIG. 1b on the same time scale as signal egi, but on aseparate time axis. It may be noted that signal es is 45 behind egl, andsignal ep, which is identical to signal PB from source 12, is 45 aheadof signal egl.

Bias voltage source 28 is connected to grid #2 of pentode 18 viaresistor 30. A bypass capacitor 32 is connected between grid #2 andground. Grid #3 is connected to ground via resistor 34. The plate ofpentode 1S is connected to output terminal 14 via lter 36.

Operation When signals A and B are in phase, the signals ep, es, and egl`will have phases as represented -by the curves in FIG. lb. During partof the interval from time t to time t2, when plate voltage ep is morepositive than grid #3 voltage es, normal plate current, represented bythe positive portion of curve ip, will ow. After es becomes greater thanep at time t2, grid #3 will collect electrons from the plate and areverse or secondary emission plate current, represented by the negativeportion of curve ip, will ow. The area under the positive portion ofcurve p should be equal to the `area included within the negativeportion so that no net plate current will flow when signals 95A and tpBare in phase. Filter 36 removes the signal frequency component of thesignal appearing on the plate, leaving only the phase indicativecomponent to be applied to output terminal 14. Since the A and hBsignals are in phase, waveform p has no D.C. component; thus no voltagewill appear at terminal 14.

Due to inherent asymmetries in the system, a D.C. voltage may appear atterminal 14 when phase coincidence does exist. This can easily beremedied by decreasing or increasing the amplitude of one of the signalsources, or by increasing or decreasing the phase shift produced by oneof the phase Shifters. For instance, if at phase coincidence, a positivevoltage appears at point 14, this indicates the positive portion of thecurrent represented by waveform ip is greater than the negative portionthereof. This can be remedied if one or more of the following be done:the alternating signal ep supplied to the plate may be decreased inamplitude, the amplitude of the lsignal es may ybe increased, the signalep may be retarded more than 90, or the signal may be retarded less than45.

Assuming that the circuit is properly adjusted, the operation whensignal A is not in phase with signal qbB will now be described. Assumethat signal pA leads signal qB. Waveform egl will be shifted to the leftin relation to waveforms ep and es as shown by the broken line cpl andthe conducting -or on intervals of tube 18 will be similarly advanced intime. The left or positive portion of waveform ip will be increasedwhile the negative portion thereof will be decreased as shown by thebroken line p; thus a net positive D.C. voltage will appear at point 14.If signal 11A lags B, a negative D.C. voltage will appear at point 14.The magnitude of the D.C. voltage, whether positive or negative, will beproportional to the magnitude of phase difference between signals 11Aand B.

In FIG. 1b, signal egl has been shown for purposes of illustration asequal in size to signals ep and es; however in practice cpl, a gridsignal, will normally be much smaller than the plate and suppressorsignals. Moreover signals es and ep have been shown as equal inamplitude, with signals es and ep respectively 45 behind and 45 ahead ofsignal cpl. It will be apparent to those skilled in the art that theinvention is not limited to these specific interrelationships betweensignals epl, es, and ep. Furthermore the signals are not limited to thesinusoidal shapes shown in the drawings; any shape repetitive waveformmay be used in accordance with the invention. The only requirementnecessary for operability is that the phase, amplitudes, and shapes ofthe signals applied to the tube be selected so that the forward (normal)and reverse (secondary emission) plate currents average to zero when thetwo input signals to be compared are in phase coincidence.

It is also seen in FIG. 1a that one of the 2 input signals (41B) issplit into two versions which are applied to the plate and suppressor,respectively. The signal which is split, may be either one of the twoinput signals, i.e., it is immaterial whether the signal which is splitis a standard phase signal or the signal of variable phase. Furthermoreit is immaterial to which two of the three tube elements (plate,suppressor, .and grid #1) the two versions of the input signal which issplit are applied, so long as the phases, amplitudes, and shapes of theapplied signals are adjusted so that the normal and reverse platecurrents average to zero when the two input signals are at phasecoincidence.

Several exemplary modications -of the conditions existing in FIGS. 1aand b will now be discussed to illustrate the foregoing principles.

FIGS. 2a, b, c--PHASE DISCRIMINATOR MODIFICATIONS FIG. 2a-ep1in phasewith es In FIGS. la and b, signals ep and es were illustrated as equallydisplaced in phase (by 45 from signal cpl. If signal es is arranged tobe closer in phase than 45 from signal egt, a concomitant shift ofsignal ep away from esl by more than 45 will still enable the normal andreverse plate currents to average to zero. This is depicted in FIG. 2a,where for purposes of simplification, signal es is illustrated as inphase with signal epl and signal ep as ahead of signal egl, althoughsimilar results will follow if signals es and ep lare made torespectively and proportionally lead signal egl by anywhere from 0 to 45and lag by `anywhere from 45 to 90. Plate current will flow under thephase conditions illustrated in the FIG. 2a substantially only fromtimes to to t2, since this interval is the only time that both signalsepi and ep are greater than cutoff and cathode potential, respectively,a condition essential for plate current ow. As shown, normal platecurrent will flow when signal ep is greater than signal es, (times t0 tot1), and reverse or `secondary emission current will flow when signal esis greater than signal ep (times t1 to t2).

The phase relationships depicted in FIG. 2a may be easily achieved forexample, by applying input signal qbA to grid #1, applying input signalB to the suppressor, and applying a 90 delayed version of either signalA or B to the plate. It should be noted that in FIG. 2a as in FIG. lb,signals ep and es are again shown as having equal amplitudes forconvenience.

FIG. ZIJ-@p1 in phase with ep; ep esg ep leads es If the signal ep isbrought closer t-o or into phase with signal egl, then signal es may beincreased in amplitude in order to enable the normal and reverse platecurrents to average lto zero. In FIG. 2b, for purposes of simpliication,signals egl and ep are illustrated as in phase, and signal es aslaggin-g by 45 Many obvious ways of shifting the phase Iand altering theamplitude of the two input signals, A and B, to produce the .conditionsshown are available and will not be discussed. The normal and reverseplate currents will average to zero from times to to t4 as shown.

FIG. ZC-epl in phase with ep; es ep; es leads ep In FIG. 2c the sameamplitude and phase relationships as in FIG. 2b are maintained with theexception that signal es leads signals egl and ep by 45 Under theseconditions the normal and reverse plate currents ip can again be made to.average to zero; it will be observed however, that the reverse platecurrent interval precedes the normal plate current interval in thisembodiment.

Many other variations of the phase position and amplitude of the threesignals, egl, es, 'and ep which will allow current p to average to zerowhen the input signals lare in phase coincidence will be apparent tothose skilled in the art and no further examples will be discussed.Accord- CHROMA REFERENCE DISCRIMINATOR APPLICATION Since the apparatusof the invention provides a phase discriminator in a simple fashionsubstantially within a single tube structure, it may advantageously be`used as a color TV chroma reference discriminator, wherein the phase ofthe incoming reference bursts is intermittently -compared with the phaseof the signal from a reference oscillator to produce an .automatic phasecontrol voltage which maintains the phase of the reference oscillatorsignal identical to that olf the incoming bursts. Referring back to FIG.la, if source represents the source of incoming bursts and source 12 thereferen-ce oscillator, the desired APC voltage will be -supplied topoint 14. The three signals, egr, es, and ep, may be derived in anymanner from the incoming burst and reference loscillator signal asIafore-discussed; the phases and amplitudes of the signals egl, es, :andep must, of course, be arranged so that no net plate current flows whenthe bursts and the reference oscillator have like phase. The signal @g1which is applied to grid #l should be derived from the bursts so thatthe pentode 18 will be conducting only when bursts are present;otherwise an APC voltage might be p-roduced when no bur-sts are beingcompared with the reference oscillator signal.

FIG. S--CHROMA REFERENCE DISCRIMINATOR BURST KEYER The circuit of FIG. 3illustrates a combined chroma reference discriminator/burst-keyerutilizing the phase discriminator of FIG. la. Because the phasediscriminator of the invention is inherently simple in Irequiring onlythree tube elements, an additional Ifunction can be performed in thesame tube structure if a multi-grid tube is utilized. In FIG. 3 thecomplete chroma signal 38 is applied to the control grid of heptode 18.To the third grid is supplied :a conventional burst keying signal 40 inphase with the bursts in signal 38. Heptode 18' can conduct only whenbur-st keying -signal 40 is present; thus a time selection function willbe performed on signal 38 so that the space current of tube 18 wil-lconfonm only to the bursts in signal 38. Signals ep and es, one or bothof which are derived from a local oscillator (L.O.), are applied to theplate and suppressorat such phase land amplitude that the plate currentwill average to zero when the bursts and the local oscillator signal arein phase. W'hen the bursts and the L.O. signal are out of phase a D.C.signal will appear at point 14 which may be employed as an automaticphase control (APC) voltage to correct the phase of the LO. signal -inconventional fash- FIG. 4-LIM-ITER/FM DISCRIMINATOR Description Thecircuit of FIG. 4a shows a single tube combined IF limiter amplifier/ FMdiscriminator utilizing the phase discriminator of the invention. AnyFM-modulated signal 40 may be applied at input 42, and the modulationsignal, which is usually of audio frequency, is obtained at output 44.

The circuit utilizes a heptode having 5 grids, g1 to g5. AnyFM-modulated carrier, represented in FIG. 4a as signal 40, is applied toinput 42, the primary of tuned transformer circuit 48. The secondary oftuned transformer circuit 48 is coupled to grid #l of tube 46 via RCIbias circuit 50. A fixed bias supply voltage 52 is coupled, viaresistor 53, to grid #2. Grid #2 function as a screen grid. Resistor 53is bypassed lby capacitor 54. Grid #3, which functions as a suppressor,is grounded, and grid #4, which functions as a plate, is coupled to oneterminal of the tuned primary winding 56 of three winding transformerS8. The other terminal of the primary winding 56 is connected to biassource 52 via resistor 53.

Transformer 58 has primary, secondary, and tertiary windings, asindicated. The transformer may be similar to those constructed fornormal 4.5 mc. discriminators or ratio detectors, and is shown, forexample, on pp. 12436 of the Radio Engineering Handbook by Henney (5thed. 1959). One side of the tertiary winding is grounded (or returned toa bias potential) and the other is center-tapped to the secondarywinding. The secondary winding, like the primary, is tuned with a shuntcapacitor. One side of the secondary winding is coupled to the plate oftu-be 46 via capacitor 60, while the other side is connected to grid #5of tube 46. Grid #5 (which usually functions as a suppressor), and theplate, correspond in functional application to the last grid and plateof tubes 18 and 18 in FIGS. la and 3, respectively.

The plate of heptode 46 is connected to one side of a conventional FMdeemphasis and iilter network 62. The other side of deemphasis network62 is connected to output terminal 44.

Operation The operation of the circuit of FIG. 4a may be most easilyunderstood if it is first noted that three functions are per-formedtherein: the cathode and first four grids of tube 46 function as alimiting amplifier; the transformer circuitry functions as afrequency-to-phase converter; and the fifth grid and plate circuitfunction as a phase comparator. These three functions will be separatelydiscussed.

(l) LIMITING AMPLIFIER The cathode and rst four grids of heptode 46 areanalogous to an ordinary pentode, with grid #4 acting as a plate. IFcarrier signal 40 is applied to tuned transformer circuit 48 at a levelsuch that sufficient limiting will occur to eliminate noise pulsestherefrom in conventional manner; the amplified and limited IF carriersignal will appear across tuned primary circuit 56 of transformer 5S.

(2) TRANSFORMER FREQUENCY-TO-PHA-SE CONVERTER Reference will be made tothe vector diagrams of the transformer waveforms in FIG. 4b to explainthe principle of operation of three winding transformer 58.

It is known that the voltage across the secondary winding of a tunedtransformer will be in quadrature with the primary voltage when thefrequency of the latter is at resonance, i.e., equal to the frequency ofthe tuned transformer. When the frequency of the primary voltagedeviates from the resonance value, the phase of the secondary voltagewill deviate from that of the primary as a linear function of suchfrequency deviation. This principle is discussed further in ModulationTheory, by Black (1953).

Thus the phase of the voltage across the entire secondary winding oftransformer S8 will be 90 behind the phase of the voltage across theprimary winding when the incoming IF carrier is unmodulated and hence isat center frequency, fo. When the carrier is modulated, its frequencywill alternately increase to a frequency (fo-l-Af) and decrease to afrequency (fo-Af), causing the phase of the secondary voltage toalternately advance and retard from its normal (carrier unmodulated)relationship. The tertiary untuned winding of transformer S8 isphysically connected so that the voltage thereacross, et will besubstantially out of phase with the primary voltage at all times.

The output voltages from transformer 58, es and ep, are derived fromterminals 61 and 64 on either side of the secondary winding. Voltage es,which is applied to grid #5, represents the vectorial sum of thetertiary voltage et and one half of the secondary winding voltage esl,measured from the centertap of the secondary winding to point 61.Voltage ep, which is applied to the plate, represents the vectorial sumof et and the other half of the secondary winding voltage, esz, measuredfrom the centertap of the secondary winding to point 64.

Vector diagram 70 in FIG. 4b, depicts the voltage on transformer 58 whenthe incoming IF carrier is at frequency fp (unmodulated). Vector el willbe 180 out of phase with the primary voltage (not shown). Vectors esland @s2 will be respectively 90 ahead of and 90 behind vector et atcenter frequency. The vectorial sum of vectors et and esl will be vectores, and vector ep will be the vectorial sum of el and es2. It should benoted that vectors es and ep are in quadrature and of equal length.

Vector diagram 72 depicts the transformer waveform when the incoming IFcarrier modulated and above center frequency, i.e., at a frequency(fo-l-Af). Vectors esl and esz will be shifted ahead causing vectors esand ep to become unequal in length, with vector ep greater than es.Vectors es and ep will remain in quadrature as shown i-f esl and esz areequal. Such a relationship may not exist in practice due to inherentasymmetries in the system.

Vector diagram 74 depicts the transformer waveforms when the frequencyof the IF carrier is at a frequency below center frequency, i.e., atfrequency (fo-Af). Here vectors es and ep will be retarded, with vectores greater than ep.

The actual waveforms of the voltages in the circuit of FIG. 4a aredepicted in FIG. 4c. It will be noted that voltages esl an-d et aresubstantially in phase over the frequency range considered. Thealternating voltages ep and es applied to the plate and grid #5,respectively, of tube 46 will `be symmetrically phase displaced fromvoltage epl at frequency fo, with es and ep in quadrature and of equalmagnitude. When the frequency of the IF carrier is a-bove or below fo,voltages ep and es will be unequal in magnitude and unequally displacedin phase with respect to voltage esl due to the transformer actionafore-discussed.

(3) PHASE COMPARATOR Grid #5 and the plate of heptode 46 function as aphase comparator which converts the phase-amplitude variations insignals es and ep into a signal representative of the modulationcomponent of signal 40. The rate of the phase-amplitude variations insignals es and ep will be proportional to the frequency of themodulating signal, While the magnitude of the phase-amplitude variationswill be proportional to the amplitude of the modulating signal.

More particularly, it can be seen in FIG. 4c that waveforms es and epare symmetrical about the vertical t2 line from times to to t4, when eplis positive. If the input signal is at frequency fo during theapproximate interval from tl to t2, when voltage ep is greater than es,normal plate current will flow as shown by the solid line fu in waveformp. From the approximate interval from time t2 to t3, secondary emissionplate current will flow as also represented by solid line fo. Since epand es are equal and symmetrically phase related to egl when the IFcarrier is at center frequency fo, the plate current z'p will average tozero. As shown in vector diagram 72 in FIG. 4b, when the frequency ofthe IF is above fo, i.e., at a frequency (ffl-Af), es and ep will beadvanced in phase position with respect to et (and egi) and magnitude ofep will increase while es will decrease. This will cause the forwardpart of plate current p to predominate over the secondary emission partthereof as shown by the dashed line fO-i-Af in waveform ip in FIG. 4c.Similarly when the frequency yof the IF carrier is below centerfrequency, i.e., at a `frequency (fo-Af) the secondary emission part ofplate current ip will predominate as will be evident from an inspectionof vector diagram 74 in FIG. 4b and dashed line )t0-Af in waveform ip.

When the IF signal is modulated, its frequency will alternately varyabove and below center frequency fo. The normal and secondary emissioncomponents of the plate current ip will alternately predominate inconformance to the frequency variations in the IF carrier, and theresulting net component of the plate current will have the same form asthe original modulating signal.

Deemphasis network 62 restores the signal components in the originalmodulating signal to their proper relationship in well-understood mannerand also removes the signal frequency components of the IF carrier fromthe plate circuit. The modulating signal, which in most cases will be ofaudio frequency, will appear at output terminal 44.

The output of the limiter-discriminator of FIG. 4a is inherentlybalanced since direct current will never appear on the plate so long asthe frequency of the IF signal applied at input 42 is equal to that towhich transformer 58 is tuned.

If the frequency of the IF signal should drift, a direct current willappear on the plate. Thus the audio output at point 44 may be used forautomatic frequency control (AFC) purposes if desired by rst filteringit to remove the audio components and then using the resultant D.C.error signal to control the frequency of the local oscillator.

FIGS. 5a AND b-MODIFICATION OF LIMITER- DISCRIMINATOR It will beapparent that signals es and ep do not have to be at the particularphase relationship shown in FIGS. 4b and c when they are applied to theplate and suppressor of tube 46. For instance the phase relationshipsshown in FIG. 2b, where ep and egl are in phase and es lags ep, may beutilized in conjunction with the circuit of FIG. 4a if transformer 58 ismodified as shown in FIG. 5a.

In FIG. 5a the ungrounded end of the tertiary winding of transformer 58is connected to point 64 and the primary-tertiary ratio is madeidentical to the primarysecondary ratio; otherwise transformer 58' andits connections are identical to transformer 58 and its connections inFIG. 4a. In FIG. 5a voltage es is equal to the vectorial sum of thevoltage et on the tertiary winding, and the voltage esec on thesecondary winding. Voltage ep is obtained at point 64 and is equal toet, the tertiary voltage. Voltage ep will not vary appreciably in phaseas the frequency of the IF carrier changes, but will have substantiallythe same phase as voltage egl except at the outer edges of thetransformer primary response curve which is beyond the range ofinterest. Voltage es, however, will vary in phase as the carrierfrequency changes as is illustrated in FIG. 5b.

Vector diagram 70 illustrates the various transformer voltages at centerfrequency fu. Voltage esec is at from both the primary voltage (notshowtn and its inversion, et, when the frequency of the IF carrier andthe frequency of the tuned transformer secondary are equal. Voltage es,the vectorial sum of et and esse, will lead et by about 45. When thefrequency of the IF carrier is above fo, i.e., at a frequency (fo-i-Af),es will advance in phase and decrease in magnitude as shown in vectordiagram 72. When the frequency of the IF carrier is below fo, i.e., at afrequency (fo-Af), es will be retarded in phase and increase inmagnitude as shown in vector diagram 74. The operation of the phasediscriminator part of the circuit for these relationships is discussedin conjunction with FIG. 2b. Various other operable phase and/oramplitude relationships between signals eg, ep, and es (including thoseof FIGS, 2a and 2c), will occur to those skilled in the art. Concomitantmodifications of transformer 58 will be, of course, required, yet thesewill be similarly obvious to those skilled in the art and hence fallwithin the scope of the invention.

The instant invention is not limited to the specificities of theforegoing description since many modifications thereof which still fallwithin the true scope of the inventive concept will be apparent to thoseconversant with 9 the art. The invention is defined only by the appendedclaims.

I claim:

1. A phase comparator for a colortelevision receiver for producing abipolar phase-error indicative signal for controlling a color referenceoscillator, comprising:

(a) an electron tube having a cathode, at least three grids including acontrol grid, a second grid, a third grid, and a plate, said third gridbeing the one closest to said plate,

(b) means connecting said cathode to a point at reference potential,

(c) means for supplying a positive bias potential to said second grid,

(d) means for supplying color reference bursts from the composite colortelevision video signal in said receiver across said control grid andsaid cathode such that space current flows in said tube to said cathodefor intermittent intervals during the duration of each applied burst,

(e) means for deriving from the output signal of the color referenceoscillator in said color television receiver two dissimilarly phasedalternating current signals of the same frequency as said output signal,

(f) means for supplying said alternating current signals to said plateand said third grid, respectively, said alternating current signalsbeing phase such that if said output signal and said color referencebursts have like phase, during one part of each said interval when spacecurrent ows said third grid will be more positive than said plate, andduring another part of each said interval said plateA will be morepositive than third grid, and

(g) alternating curernt filter means connected to said plate, forpassing, a bipolar phase-error indicative output signal from saidcomparator while suppressing the burst-frequency component of the signalat said plate.

2. The comparator of claim 1 wherein said electron tube includes afourth grid interposed between said second grid and said control grid,said means of clause (d) is arranged to supply said composite colortelevision videoY signal, including said color reference bursts, acrosssaid control grid and said cathode, and wherein said comparator furtherincludes means for supplying a burst keying signal to said fourth gridso as to enable said tube to conduct only during intervals when saidcolor bursts are present, whereby said phase comparator will alsofunction as a burst keyer.

3. A frequency modulation detector comprising:

(a) a vacuum tube having a cathode, at least three grids, and a plate,

(b) means connecting said cathode to a point at reference potential,

(c) means for impressing a carrier signal which is frequency modulatedby an intelligence signal on a first of said grids,

(d) means for deriving said carrier signal from a second of said gridsin amplified form,

(e) means for deriving from said amplified carrier signal two furthersignals of like frequency as said carrier signal but of dissimilarphase,

(f) means for impressing one of said two further signals on a third ofsaid grids and for impressing the other of said two further signals onsaid plate, said two further signals having phases such that said thirdgrid will alternately be more positive than said plate at the frequencyof said carrier, and

(g) filter means for deriving said intelligence signal from said platewhile suppressing the carrier frequency component of the `signal at saidplate.

4. A frequency modulation detector comprising:

(a) a vacuum tube having at least four grids, a plate,

and a cathode connected to reference potential,

(b) means for supplying to a first of said grids a carrier signal whichis frequency modulated by an intelligence signal,

(c) a transformer having a primary winding connected between a secondand a third of said grids, said primary winding also being connected toa biasing source, whereby an amplified version of said carrier signalwill be supplied across said primary winding,

(d) said transformer having a tuned secondary winding inductivelycoupled to said primary winding for developing oppositely-phasedversions of said carrier signal,

(e) means for supplying a reference signal having a phase in quadraturewith said oppositely-phased versions of said carrier signal,

(f) means for adding said reference signal and one of saidoppositely-phase signals and for supplying the resultant sum signal tothe plate of said vacuum tube, and for adding said reference signal andthe other of said oppositely-phase signals and for supplying theresultant sum signal to a fourth of said grids so as to cause normal andsecondary emission currents to ow alternately to and from said plate,and

(g) filter means for passing said intelligence signal from said platewhile suppressing the carrier frequency component of the signal at saidplate.

S. An intermediate frequency limiting amplifier and frequency modulationdetector comprising, in combination:

(a) a heptode having a cathode, plate, and 5 grids,

consecutively numbered from cathode to plate,

(b) a source of frequency modulated intermediate frequency carriersignal connected between grid #l and said cathode,

(c) means connecting grid #3 to a source of reference potential,

(d) a 3-winding transformer having primary, secondary, and tertiarywindings, said secondary winding being tuned to said intermediatefrequency, said primary winding being connected between grid #2 and grid#4, said tertiary winding being connected between ground and a centertapon said secondary winding, and said secondary winding being connectedbetween grid #5 and said plate, and

(e) an output terminal also connected to said plate for deriving ademodulated output, signal therefrom.

References Cited by the Examiner UNITED STATES PATENTS 2,585,532 2/1952Briggs 329-137 3,028,559 4/1962 Spacklen 329-138 X 3,192,314 6/1965Taylor 178-5.8

DAVID G. REDINBAUGH, Primary Examiner.

J. H. SCOTT, Assistant Examiner.

1. A PHASE COMPARATOR FOR A COLOR TELEVISION RECEIVER FOR PRODUCING ABIPOLAR PHASE-ERROR INDICATIVE SIGNAL FOR CONTROLLING A COLOR REFERENCEOSCILLATOR, COMPRISING: (A) AN ELECTRON TUBE HAVING A CATHODE, AT LEASTTHREE GRIDS INCLUDING A CONTROL GRID, A SECOND GRID, A THIRD GRID, AND APLATE, SAID THIRD GRID BEING THE ONE CLOSEST TO SAID PLATE, (B) MEANSCONNECTING SAID CATHODE TO A POINT AT REFERENCE POTENTIAL, (C) MEANS FORSUPPLYING A POSITIVE BIAS POTIENTIAL TO SAID SECOND GRID, (D) MEANS FORSUPPLYING COLOR REFERENCE BURSTS FROM THE COMPOSITE COLOR TELEVISIONVIDEO SIGNAL IN SAID RECEIVER ACROSS SAID CONTROL GRID AND SAID CATHODESUCH THAT SPACE CURRENT FLOWS IN SAID TUBE TO SAID CATHODE FORINTERMITTENT INTERVALS DURING THE DURATION OF EACH APPLIED BURST, (E)MEANS FOR DERIVING FROM THE OUTPUT SIGNAL OF THE COLOR REFERENCEOSCILLATOR IN SAID COLOR TELEVISION RECEIVER TWO DISSIMILARLY PHASEDALTERNATING CURRENT SIGNALS OF THE SAME FREQUENCY AS SAID OUTPUT SIGNAL(F) MEANS FOR SUPPLYING SAID ALTERNATING CURRENT SIGNALS TO SAID PLATEAND SAID THIRD GRID, RESPECTIVELY, SAID ALTERNATING CURRENT SIGNALSBEING PHASE SUCH THAT IF SAID OUTPUT SIGNAL AND SAID COLOR REFERENCEBURSTS HAVE LIKE PHASE, DURING ONE PART OF EACH SAID INTERVAL WHEN SPACECURRENT FLOWS SAID THIRD GRID WILL BE MORE POSITIVE THAN SAID PLATE, ANDDURING ANOTHER PART OF EACH SAID INTERVAL SAID PLATE WILL BE MOREPOSITIVE THAN THIRD GRID, AND (G) ALTERNATING CURRENT FILTER MEANSCONNECTED TO SAID PLATE, FOR PASSING, A BIPOLAR PHASE-ERROR INDICATIVEOUTPUT SIGNAL FROM SAID COMPARATOR WHILE SUPPRESSING THE BURST-FREQUENCYCOMPONENT OF THE SIGNAL AT SAID PLATE.